This invention relates to a powertrain for hybrid electric vehicles that carry two drive sources, an internal combustion engine and electric motor on board.
The hybrid electric vehicle is propelled by one or both of the internal combustion engine and the electric motor, running according to driving conditions so as to reduce the air pollution resulting from the internal combustion engine and improve the fuel economy.
Such a type of the hybrid vehicle is shown in xe2x80x9cAutomotive Engineering/July 1997xe2x80x9d (page 56-58). This powertrain includes an internal combustion engine, an electric motor, an electric generator, a battery and a power-split device. The power-split device consists of one planetary gear set: it has a sun gear, a ring gear (an internal teethed gear), a planetary carrier. The ring gear is coaxial with the sun gear and the planetary carrier. The planetary carrier supports rotatably pinions meshing with both of the sun gear and the ring gear. The sun gear is connected to the generator, the ring gear to the motor, and the planetary carrier to the engine.
Its Operations are as follows:
Startup, low-speed and low-speed deceleration operation: The battery supplies the electric motor with electricity to propel the vehicle. The engine is stopped by fuel cut-off because its load is low in this operation.
Normal operation: The power-split device divides engine""s output, one part driving the vehicle and the other driving the generator to supply its electric output to the motor. The motor adds its output to the propulsion of the vehicle in addition to the power of the engine.
Full-throttle operation: The engine"" full power is provided to the vehicle""s wheels. In addition, the motor, supplied with electricity from the battery, drives wheels to augment the drive power.
The above type of the prior powertrain, however, has following drawbacks:
In the normal operation, its maximum torque is not so large to drive medium- and heavy-duty vehicles such as commercial cars, buses or trucks. Besides its fuel efficiency is low.
The reason is as follows: As one part of engine""s output is divided by the power-split device to drive the generator for supplying its electric output to the motor in the normal operation, the total efficiency includes a mechanical transmitting efficiency of the power-split device, an electricity-generating efficiency of the generator, an electricity-transmitting efficiency between the generator and the motor and a driving efficiency of the motor. This effects fuel consumption worse than vehicles with only a mechanical transmission.
Besides the power-split device has no ability to increase the engine""s torque enough for driving medium- and heavy-duty vehicles.
It is an object of the invention to provide a powertrain for hybrid electric vehicles that can obtain a large torque enough for driving medium- and heavy-duty vehicles such as trucks and commercial vehicles.
It is another object of the invention to provide a powertrain for hybrid electric vehicles that can reduce fuel consumption.
It is still another object of the invention to provide a powertrain for hybrid electric vehicles with a compact powertrain.
For the above purposes, in accordance with the present invention, there is provided a powertrain for hybrid electric vehicles comprising an internal combustion engine, an input shaft connected to the engine, an output shaft, a plural sets of planetary gear sets between the input shaft and the output shaft, a first electric motor/generator and a second electric motor/generator.
The planetary gear sets include a first planetary gear set and a second planetary gear set. The first planetary gear set has a first rotatable member, and the second planetary gear set has a second rotatable member. The first rotatable member establishes a reduced speed ratio when it is braked, and the second rotatable member establishes an overdrive speed ratio when it is braked. The first electric motor/generator is connectable with the first rotatable member. The second electric motor/generator is connectable selectively with the second rotatable member or with the output shaft.
Preferably, the plural sets of planetary gear sets may comprise two sets, the first planetary gear set and the second planetary gear set. The second planetary gear set has a driving member connectable with the second rotatable member via an idle gear.
Preferably, the driving member may be connected with a shaft of a power take-off device.
Preferably, the plural sets of planetary gear sets may comprise three sets, the first planetary gear set, the second planetary gear set, and a third planetary gear set. The third planetary gear set has a third rotatable member to establish a medium speed ratio when it is braked. And the first electric motor/generator is connectable selectively with the first and second rotatable members, and the second electric motor/generator being connectable to selectively with one of the output shaft and the third rotatable member.
Preferably, the one of the planetary gear sets may be positioned to a first shaft, and the other to a second shaft parallel to the first shaft.